1. Field of the Invention
The present invention relates to a lighting apparatus which is mounted, for example, to a data reader which reads coded data such as two-dimensional data symbols.
2. Description of the Related Art
In a known POS (Point-of-Sale) system, a bar code reader (optical scanner) reads a bar code which represents sales data. The bar code which is in the form of a series of lines of varying width is scanned perpendicular to the direction in which the lines were drawn, by laser beams. However, not much data can be obtained from the bar code using this one-dimensional scanning method.
In order to provide much more data, a two-dimensional data symbol consisting of a two-dimensional matrix (mosaic pattern) of, for example, white and black segments has been recently proposed and used. However, there are few simple data readers available, particularly those kinds using an area sensor to read the two-dimensional data symbols.
In order to simultaneously read two-dimensional data symbols placed in orthogonal directions within a plane, it is necessary to uniformly illuminate the two-dimensional data symbols in the orthogonal directions. Accordingly, if a conventional lighting apparatus which has been used for a data reader for one-dimensional data symbols to uniformly illuminate the latter only in one direction, is used for the two dimensional symbol data, it is impossible to uniformly illuminate the latter in the orthogonal directions. Hence, in an attempt to develop a data reader for two-dimensional data symbols, it is necessary to realize a lighting apparatus which can simultaneously and uniformly illuminate two-dimensional data symbols within a data reading area which is drawn on a single plane.
Furthermore, if the light emitted from the light source is reflected within the data reading area and reaches the CCD, a spurious image of the light source is formed on the CCD, thus resulting in a failure to correctly read the data.
To solve these problems, it is necessary to provide an appropriate angle between the optical axis of the illumination light and a line normal to a reference surface on which the two-dimensional data symbols are formed within the data reading area.
However, if there is a large angle of inclination of the optical axis of the illumination light with respect to the normal line to the reference surface, the lateral size of the lighting apparatus is increased, leading to a large data reading apparatus.